When contributing to the reading guide, follow these steps:
1) First complete the reading guide on your own from the evolution unit page. 2) Write your response to a question in word and then copy it. 3) Click on the edit button and then go to the appropriate question and paste your answer below it.Sign your contribution with your first name and last initial. 4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Then click Save.
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Guided Reading Chapter 23
1. Define the following terms:
a. Microevolution: evolutionary change below the species level; change in the genetic makeup of a population from generation to generation. It is evolutionary change on its smallest scale
b. Population: a localized group of individuals that belong to the same biological species, capable of interbreeding and producing viable offspring.
c. Population genetics: the study of how populations change genetically over time.
d. Gene pool: the total aggregate of genes in a population at any one time. It consists of all alleles at all gene loci in all individuals of the population
-- Brian N
2. What is the Hardy-Weinberg Theorem and why does it appear to be an apparent contradiction to evolution?
The theorem states that frequencies of alleles and genotypes will stay the same as long as the gametes are contributed to the next population at random. This appears to be a contradiction to evolution because it seems to say populations will never change. However, this condition only exists under certain conditions which do not apply to the majority of populations. The five conditions are: 1. Extremely large population size. 2. No gene flow. 3. No mutations. 4. Random Mating 5. No natural selection.
3. What is Hardy-Weinberg equilibrium?
Hardy-Weinberg equilibrium is the condition describing a non-evolving population (one that is in genetic equilibrium).
4. Use the blank diagram below to relate the H-W equation to a Punnett square.
The H-W theory completely disproves any Pre-Mendelian theories, when the concept of inheritance was not yet understood. Before there was inheritance, there was a blending theory. Therefore, if a red flower mated with a white flower, their offspring would essentially “blend”, creating a paler red, or pink, flower. In this case, genetic variation would not exist because the two factors in the parents only produce one factor in the offspring. Therefore, no inheritance would ever exist because the blending would eventually create a uniform population of flowers.
Interesting and accurate answer. The question was really looking for a modified diagram like the one in #2. - MrV
5. What are the five conditions for H-W equilibrium to maintained?
Extremely large population size
No gene flow
No mutations
Random mating
5. No natural selection
6. How can the H-W equation be used to today in terms of human health? The Hardy-Weinburg equation can be used to estimate percentages of humans that carry alleles which lead to inheritable diseases. If you have the percentage of people with a disease and if you know weather the disease is recessive than it is easy to find the percentage of a population that are carriers of the disease. With this information one can predict how the disease will affect a population in the future.
7. What are the two broad processes that make evolution possible? The two broad processes that make evolution possible are mutation and sexual recombination.
–Jackie H.
8. What is the impact of the following:
a. Point mutation Has impact in phenotype, like a sickle cell disease, most however are harmless. A reason for this is that much DNA in eukaryotic genomes do not code for protein products. Because the genetic code is redundant, point mutations in genes may have little effect because they do not alter proteins amino acids.
-Stephanie It is a change in one base in a gene. Most point mutations are harmless because DNA in eukaryotic genomes does not code for protein products. Point mutations in genes that code for protein have little effect because it does not change the amino acid composition of that protein. Some non coding regions of DNA to regulate genes. Mutations often hinder an organism but can help of rare occasions usually when the environment changes to give the mutation the upper hand in the new environment. An example would be squirrels freezing when scared. This caused them to get run over by cars making the recessive gene for the squirrel to keep running become useful. b. Gene duplication Duplications, deletion and rearrangement of chromosome segments are almost always harmful but if it leaves that gene intact it may be neutral and in rare cases beneficial. DNA is introduced to a new genome through activity of transposable elements. If the duplicated segment does not have a negative effect it can continue over generations providing an expanded genome that may take on new function. New genes may also come to be when the coding portion of a gene or exon is shuffled within the genome.
c. Sexual Recombination Sexual recombination shuffles the alleles in the gene pool. There are countless different combinations of genes that can be recombined into many different variations. This helps a population making all individuals a little be different because then if there is a problem such as a disease. There is a better chance that the disease will only affect a small portion of the population. This alters everyones phenotypes.
Adam A, Mario C, Martin A
9. What is the relationship between mutation rates and generation span?
The mutation rates rise as the generation spans decrease. In animals and plants, there is only about one mutation in every 100,000 genes per generation.
Adam A, Mario C, Martin A
10. Define the following:
Genetic drift: unpredictable fluctuations in allele frequencies, reduces genetic variation over time through such losses of alleles Bottleneck effect: when environmental change greatly reduces a population, the ratio of genes is mixed up. Certain alleles may be over/underrepresented among the survivor. Usually occurs from a natural disaster.
Founder effect: isolated individuals of a population establish a new population → limited gene pool Gene flow: genetic additions and/or subtractions from a population resulting from the movement of gametes
Adam A, Mario C, Martin A 11. Why would we discuss adaptive evolution and what role does natural selection play?
Adaptive evolution is what allows organisms to live in changing environments. Adaptations are the result of natural selection. Natural selection allows organisms to adapt to changing environments so they can benefit from an environment.
Adam A, Mario C, Martin A
12. Give examples of phenotypical variation that is not inheritable. -A common example is bodybuilders. Bodybuilders alter their phenotypes dramatically but do not pass their huge muscles on to the next generation.
13. Explain the terms phenotypic polymorphism and genetic polymorphism in common terms giving an example from your own experience. I will be looking for a reasonable answer for this question.
14. How do we measure genetic variation?
We measure genetic variation based on the average heterozygosity. This is the average percent of a species/population that are heterozygous.
-Steve W.-
15. How can very small differences in nucleotide sequences lead to such diversity in the human population?
16. What is geographic variation and how does the term cline relate?
17. What is different about the terms fitness and relative fitness?
Fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.
Relative fitness is the contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus.
Jim Raciti
18. Why is it said that evolution acts on phenotypes and not genotypes?
19. Use the diagram below to differentiate between the modes of selection.
Directional SelectionDisruptive Selection Stabilizing Selection
Directional selection shifts the frequency curve for some phenotypic character in one direction or the other by favoring individuals that deviate from the average. Disruptive selection occurs when conditions favor individuals on both extremes of a phenotypic range over individuals with intermediate phenotypes. Stabilizing selection acts against extreme phenotypes and favors intermediate variants.
20. Why does diploidy preserve genetic variation? Diploidy preserves genetic variation because instead of giving you the same exact 46 chromosomes as one of your parents you get 23 from each making up an entire set for a new living creature. By doing so you have less of a chance of receiveing the same exact genes your parents did.
21. How does balancing natural selection relate to the term balanced polymorphism?
22. Define and give an example of the following:
a. Heterozygote advantage—Gender reproductive success of heterozygous individuals compared to homozygote; it tends to preserve variation in gene pools Ex.: Heterozygous protection from the disease malaria in Africa.
When the heterozygote genotype possesses higher relative fitness than either the homozygous dominant or homozygous recessive genotypes
An example is a human with genes heterozygous for sickle-cell anemia; they are not affected by the harmful symptoms of the disease, yet are protected against most forms of malaria.
b. Frequency dependent selection— it is when the fitness of any one morph declines if it becomes too common in the population. Ex.: If almost all red flowers declined in number, most insects would eat the white flowers then they will become rare also.
c. Neutral variation-- genetic diversity that confers no apparent selective advantage. Ex.: If my DNA was mutated, I might not know it. Could stay recessive and dormant in my genes; it wound not effect my selective advantage.
d. Sexual dimorphism-- marked differences between the sexes in secondary sexual characteristics which are not directly associated with reproduction. Ex.: When individuals (mostly the males) have flashy characteristics about themselves that helps make sure they get a mate. Like Peacock feathers.
e. Intrasexual selection-- selection “with-in the same sex” is a direct competition among individuals of one sex for mates of the opposite sex. Ex.: When rams buck heads to show the female that they are the stronger and more worthy of a mate than the loser.
f. Intersexual selection-- mate choice, individuals of one sex are choosy in selecting their mates from the other sex. Ex.: The female’s choice depends on the showiness of the male’s appearance or how they behave.
23. What are the limitations to Natural Selection
1.Evolution is limited by historical constraints. This means that a species cannot completely start fresh. New species are simply modifications of preexisting species. 2.Adaptations are often compromises. One adaptation may cause problems in certain aspects while also causing serious advantages (ex: a human is very flexible making it athletic, but humans, because of this, are very prone to torn ligaments and serious joint injuries). 3.Chance and natural selection interact. 4.Selection can only edit existing variations.
Natural selection will never be able to create the “ideal” organism because in part, the process is not perfect. Quirks such as genetic drift, modified ancestral anatomy, the limited amount of available variation will always restrict organisms from becoming the perfect beings.
1) First complete the reading guide on your own from the evolution unit page.
2) Write your response to a question in word and then copy it.
3) Click on the edit button and then go to the appropriate question and paste your answer below it. Sign your contribution with your first name and last initial.
4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Then click Save.
Guided Reading Chapter 23
1. Define the following terms:
a. Microevolution: evolutionary change below the species level; change in the genetic makeup of a population from generation to generation. It is evolutionary change on its smallest scale
b. Population: a localized group of individuals that belong to the same biological species, capable of interbreeding and producing viable offspring.
d. Gene pool: the total aggregate of genes in a population at any one time. It consists of all alleles at all gene loci in all individuals of the population
-- Brian N
2. What is the Hardy-Weinberg Theorem and why does it appear to be an apparent contradiction to evolution?
The theorem states that frequencies of alleles and genotypes will stay the same as long as the gametes are contributed to the next population at random. This appears to be a contradiction to evolution because it seems to say populations will never change. However, this condition only exists under certain conditions which do not apply to the majority of populations. The five conditions are: 1. Extremely large population size. 2. No gene flow. 3. No mutations. 4. Random Mating 5. No natural selection.
3. What is Hardy-Weinberg equilibrium?
Hardy-Weinberg equilibrium is the condition describing a non-evolving population (one that is in genetic equilibrium).
4. Use the blank diagram below to relate the H-W equation to a Punnett square.
The H-W theory completely disproves any Pre-Mendelian theories, when the concept of inheritance was not yet understood. Before there was inheritance, there was a blending theory. Therefore, if a red flower mated with a white flower, their offspring would essentially “blend”, creating a paler red, or pink, flower. In this case, genetic variation would not exist because the two factors in the parents only produce one factor in the offspring. Therefore, no inheritance would ever exist because the blending would eventually create a uniform population of flowers.
Interesting and accurate answer. The question was really looking for a modified diagram like the one in #2. - MrV
5. What are the five conditions for H-W equilibrium to maintained?
- Extremely large population size
- No gene flow
- No mutations
- Random mating
5. No natural selection6. How can the H-W equation be used to today in terms of human health?
The Hardy-Weinburg equation can be used to estimate percentages of humans that carry alleles which lead to inheritable diseases. If you have the percentage of people with a disease and if you know weather the disease is recessive than it is easy to find the percentage of a population that are carriers of the disease. With this information one can predict how the disease will affect a population in the future.
7. What are the two broad processes that make evolution possible?
The two broad processes that make evolution possible are mutation and sexual recombination.
–Jackie H.
8. What is the impact of the following:
a. Point mutation
Has impact in phenotype, like a sickle cell disease, most however are harmless. A reason for this is that much DNA in eukaryotic genomes do not code for protein products. Because the genetic code is redundant, point mutations in genes may have little effect because they do not alter proteins amino acids.
-Stephanie
It is a change in one base in a gene. Most point mutations are harmless because DNA in eukaryotic genomes does not code for protein products. Point mutations in genes that code for protein have little effect because it does not change the amino acid composition of that protein. Some non coding regions of DNA to regulate genes. Mutations often hinder an organism but can help of rare occasions usually when the environment changes to give the mutation the upper hand in the new environment. An example would be squirrels freezing when scared. This caused them to get run over by cars making the recessive gene for the squirrel to keep running become useful.
b. Gene duplication
Duplications, deletion and rearrangement of chromosome segments are almost always harmful but if it leaves that gene intact it may be neutral and in rare cases beneficial. DNA is introduced to a new genome through activity of transposable elements. If the duplicated segment does not have a negative effect it can continue over generations providing an expanded genome that may take on new function. New genes may also come to be when the coding portion of a gene or exon is shuffled within the genome.
c. Sexual Recombination
Sexual recombination shuffles the alleles in the gene pool. There are countless different combinations of genes that can be recombined into many different variations. This helps a population making all individuals a little be different because then if there is a problem such as a disease. There is a better chance that the disease will only affect a small portion of the population. This alters everyones phenotypes.
Adam A, Mario C, Martin A
9. What is the relationship between mutation rates and generation span?
The mutation rates rise as the generation spans decrease. In animals and plants, there is only about one mutation in every 100,000 genes per generation.
Adam A, Mario C, Martin A
10. Define the following:
Genetic drift: unpredictable fluctuations in allele frequencies, reduces genetic variation over time through such losses of alleles
Bottleneck effect: when environmental change greatly reduces a population, the ratio of genes is mixed up. Certain alleles may be over/underrepresented among the survivor. Usually occurs from a natural disaster.
Founder effect: isolated individuals of a population establish a new population → limited gene pool
Gene flow: genetic additions and/or subtractions from a population resulting from the movement of gametes
Adam A, Mario C, Martin A
11. Why would we discuss adaptive evolution and what role does natural selection play?
Adaptive evolution is what allows organisms to live in changing environments. Adaptations are the result of natural selection. Natural selection allows organisms to adapt to changing environments so they can benefit from an environment.
Adam A, Mario C, Martin A
12. Give examples of phenotypical variation that is not inheritable.
-A common example is bodybuilders. Bodybuilders alter their phenotypes dramatically but do not pass their huge muscles on to the next generation.
13. Explain the terms phenotypic polymorphism and genetic polymorphism in common terms giving an example from your own experience. I will be looking for a reasonable answer for this question.
14. How do we measure genetic variation?
We measure genetic variation based on the average heterozygosity. This is the average percent of a species/population that are heterozygous.
-Steve W.-
15. How can very small differences in nucleotide sequences lead to such diversity in the human population?
16. What is geographic variation and how does the term cline relate?
17. What is different about the terms fitness and relative fitness?
Fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.
Relative fitness is the contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus.
Jim Raciti
18. Why is it said that evolution acts on phenotypes and not genotypes?
19. Use the diagram below to differentiate between the modes of selection.
Directional Selection Disruptive Selection Stabilizing Selection
Directional selection shifts the frequency curve for some phenotypic character in one direction or the other by favoring individuals that deviate from the average.
Disruptive selection occurs when conditions favor individuals on both extremes of a phenotypic range over individuals with intermediate phenotypes.
Stabilizing selection acts against extreme phenotypes and favors intermediate variants.
20. Why does diploidy preserve genetic variation?
Diploidy preserves genetic variation because instead of giving you the same exact 46 chromosomes as one of your parents you get 23 from each making up an entire set for a new living creature. By doing so you have less of a chance of receiveing the same exact genes your parents did.
21. How does balancing natural selection relate to the term balanced polymorphism?
22. Define and give an example of the following:
a. Heterozygote advantage—Gender reproductive success of heterozygous individuals compared to homozygote; it tends to preserve variation in gene pools Ex.: Heterozygous protection from the disease malaria in Africa.
When the heterozygote genotype possesses higher relative fitness than either the homozygous dominant or homozygous recessive genotypes
An example is a human with genes heterozygous for sickle-cell anemia; they are not affected by the harmful symptoms of the disease, yet are protected against most forms of malaria.
b. Frequency dependent selection— it is when the fitness of any one morph declines if it becomes too common in the population. Ex.: If almost all red flowers declined in number, most insects would eat the white flowers then they will become rare also.
c. Neutral variation-- genetic diversity that confers no apparent selective advantage. Ex.: If my DNA was mutated, I might not know it. Could stay recessive and dormant in my genes; it wound not effect my selective advantage.
d. Sexual dimorphism-- marked differences between the sexes in secondary sexual characteristics which are not directly associated with reproduction. Ex.: When individuals (mostly the males) have flashy characteristics about themselves that helps make sure they get a mate. Like Peacock feathers.
e. Intrasexual selection-- selection “with-in the same sex” is a direct competition among individuals of one sex for mates of the opposite sex. Ex.: When rams buck heads to show the female that they are the stronger and more worthy of a mate than the loser.
f. Intersexual selection-- mate choice, individuals of one sex are choosy in selecting their mates from the other sex. Ex.: The female’s choice depends on the showiness of the male’s appearance or how they behave.
23. What are the limitations to Natural Selection
1. Evolution is limited by historical constraints. This means that a species cannot completely start fresh. New species are simply modifications of preexisting species.
2. Adaptations are often compromises. One adaptation may cause problems in certain aspects while also causing serious advantages (ex: a human is very flexible making it athletic, but humans, because of this, are very prone to torn ligaments and serious joint injuries).
3. Chance and natural selection interact.
4. Selection can only edit existing variations.
Natural selection will never be able to create the “ideal” organism because in part, the process is not perfect. Quirks such as genetic drift, modified ancestral anatomy, the limited amount of available variation will always restrict organisms from becoming the perfect beings.